Conventionally, cutting fluid such as cutting oil or water soluble coolant has been supplied to the cutting portion (cutting blade or cut material) in order to lubricate and cool the cutting portion in a rotary cutting process. Supplying cutting fluid to the cutting portion has been performed by an external supply method in which cutting fluid is supplied from outside the rotary cutting tool, as well as by an internal supply method in which cutting fluid is supplied from a hole that is formed in the rotary cutting tool (see Japanese Unexamined Patent Application Publication No. 2003-181743, Japanese Utility Model Application Publication No. H7-35699, Japanese Utility Model Application Publication No. H5-13476).
The supply path for the cutting fluid in the internal supply method is preferably a center-type supply path in which the center of the fluid path is located through the center of rotation. In the case of a center-type supply path, connection of the supply path from a non-rotating section to a rotating section can be performed relatively easily, and it is possible to reduce the effect of centrifugal force on the fluid that flows through the supply path.
However, a center-type supply path is limited to mechanical construction having a path that penetrates completely through the center of rotation, making the range of application narrow. Therefore, a peripheral-type supply path is employed that supplies cutting fluid from the perimeter separated from the center of rotation of the tool supporting end of the rotating shaft, and pulls in the supply path toward the center of rotation inside the cutter.
In the case of a peripheral-type supply path, the path is not limited to mechanical construction that rotates and drives a rotary cutting tool, so the path can be widely applied to use in various kinds of rotary type machine tools such as existing lathes and the like. However, in the case of a peripheral-type supply path, connection of the supply path from a non-rotating section to a rotating section must be performed at a location that is separated from the center of rotation by a specified radius, and the supply path may need to bend in at least one location. In addition, a supply path that is separated from the center of rotation also has the disadvantage in that the effect of centrifugal force on the fluid flowing inside the flow path is relatively large.
Recently, supplying a combination of cutting fluid and air in the form of a mist is advantageous. By supplying cutting fluid in the form of a mist, it is possible to uniformly supply cutting fluid to the cutting portion using only a small amount of fluid, which not only improves processing efficiency and life of the cutting tool, but also makes it possible to conserve on cutting fluid and promote the improvement of cleanliness and work efficiency, as well as makes it possible to supply a mixture of oil mist and water mist.
However, in order to supply a combination of cutting fluid and air in the form of a mist in a conventional rotary cutter having a peripheral-type supply path, there are the following problems.
In a convention rotary cutter having a peripheral-type supply path, even though a combination of cutting oil and air in the form of a mist is supplied from around the principal rotating shaft, mist is not sprayed well from a spray orifice that is provided on the tip end section of the rotary cutting tool, with part sometimes being output in liquid form, or mist is sprayed intermittently or in a pulse-like manner, making it difficult to spray mist stably and steadily. Moreover, due to that effect, it is difficult to reduce the diameter of the supply path inside the rotary cutting tool, and thus it is difficult to apply this type of supply path to small diameter rotary cutting tools.
The reason that the mist spray become unstable is that mist that is supplied from the perimeter of the main rotating shaft returns to a liquid form when it comes in contact with the inner wall of the supply path due to centrifugal force, and cutting fluid that builds up inside the supply path after returning to a liquid form affects the flow of the cutting fluid in mist form so the output of mist becomes intermittent and pulse-like, causing an unstable mist spray.
Even by increasing the supply pressure of the mist in order to overcome the effect of the centrifugal force, mist still returns to the liquid form when the mist comes in contact with the inner wall of a bent or curved portion of the supply path, so it is difficult to avoid the same result.